System for testing charge trap memory cells

ABSTRACT

A circuit for testing a memory includes a complementary charge trap memory cell, which includes a first transistor and a second transistor. A logical value of the cell corresponds to respective states of the first transistor and the second transistor. The circuit further includes a first bitline coupled to the first transistor, where the first transistor is configured to apply a first voltage to the first bitline. The circuit includes a second bitline coupled to the second transistor, where the second transistor is configured to apply a second voltage to the second bitline. The circuit also includes a sense circuit configured to output, prior to programming of the complementary charge trap memory cell, a logical high signal or a logical low signal in response to the first voltage on the first bitline and the second voltage on the second bitline.

I. FIELD OF THE DISCLOSURE

The present disclosure relates generally to computing systems, and more particularly, to circuitry for testing charge trap memory.

II. BACKGROUND

A charge trap memory may include charge trap memory cells, each having two or more transistors. The charge trap memory may be coupled to a sense circuit to generate outputs corresponding to the logical states of the charge trap memory cells during a read operation.

The logical state of a particular charge trap memory cell may be based on the respective states of its transistors. The transistors may be associated with respective voltage thresholds, and differences between the respective voltage thresholds may exist due to certain imperfections in manufacturing of the transistors. Prior to programming of the particular charge trap memory cell, the magnitudes of the differences in the voltage thresholds may be unknown and/or undetectable. Because the respective voltage thresholds correspond to the states of the transistors, and because their differences in magnitude are unknown prior to programming, the logical state of the particular charge trap memory cell is also unknown prior to programming. As a result, without a known logical state of the particular charge trap memory cell, testing the output of the sense circuit may be difficult.

III. SUMMARY OF THE DISCLOSURE

A circuit for testing a memory includes a complementary charge trap memory cell. The complementary charge trap memory cell includes a first transistor and a second transistor, and a logical value of the cell corresponds to respective states of the first transistor and the second transistor. The circuit further includes a first bitline coupled to the first transistor, where the first transistor is configured to apply a first voltage to the first bitline. The circuit includes a second bitline coupled to the second transistor, where the second transistor is configured to apply a second voltage to the second bitline. The circuit also includes a sense circuit configured to output, prior to programming of the complementary charge trap memory cell, a logical high signal or a logical low signal in response to the first transistor applying the first voltage to the first bitline and the second transistor applying the second voltage to the second bitline.

According to another embodiment, a method includes applying a first voltage to a first bitline via a first transistor of a charge trap memory cell. The method also includes applying a second voltage to a second bitline via a second transistor of the charge trap memory cell. The method further includes outputting, prior to programming of the charge trap memory cell, a logical high signal or a logical low signal in response to applying the first voltage to the first bitline and the second voltage to the second bitline.

According to another embodiment, a computer-readable storage device includes computer-executable instructions, that when executed by at least one processor, causes the at least one processor to perform operations. The operations include applying a first voltage to a first bitline via a first transistor of a charge trap memory cell. The operations also include applying a second voltage to a second bitline via a second transistor of the charge trap memory cell. The operations further include outputting, prior to programming of the charge trap memory cell, a logical high signal or a logical low signal in response to applying the first voltage to the first bitline and the second voltage to the second bitline.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a system for testing charge trap memory cells, according to one embodiment;

FIG. 2 is a block diagram showing another particular embodiment of a system for testing charge trap memory cells;

FIG. 3 is a flow diagram of a method for testing charge trap memory cells according to a particular embodiment.

FIG. 4 is a block diagram showing a general computing system for testing charge trap memory cells according to a particular embodiment.

V. DETAILED DESCRIPTION

In the present disclosure, an embodiment of a system for testing operation of a charge trap memory is disclosed. The system may include the charge trap memory, which may include a plurality of charge trap memory cells. Further, each charge trap memory cell may include two or more transistors. The system may also include a sense circuit coupled to one or more of the charge trap memory cells, such as via one or more bitlines. The sense circuit may be configured to generate, for each charge trap memory cell that is being read, an output signal corresponding to the logical state of the charge trap memory cell. For instance, if a read operation is initiated for a particular charge trap memory cell and its logical state is a logical high, the sense circuit may be configured to generate an output signal that corresponds to the logical high of the particular charge trap memory cell.

Prior to programming of the particular charge trap memory cell of the charge trap memory, the logical state of the particular charge trap memory cell may be unknown. For instance, due to imperfections during manufacturing, there may be differences between respective voltage thresholds associated with the transistors in the particular charge trap memory cell. However, the differences between the voltage thresholds may be unknown prior to programming of the particular charge trap memory cell. The voltage thresholds affect the state of the transistors. As a result, the logical state of the particular charge trap memory cell may be unknown. Consequently, testing an output signal of the sense circuit may be difficult because the output signal cannot be compared against a known logical state of the particular charge trap memory cell.

According to a particular embodiment, a particular complementary charge trap memory cell may include a first transistor and a second transistor. Further, the logical value of the particular complementary charge trap memory cell may correspond to respective states of the first transistor and the second transistor. For instance, the logical value of the particular complementary charge trap memory cell may represent a logical high in response to the state of the first transistor being a logical low and the state of the second transistor being a logical high. Conversely, the logical value of the particular complementary charge trap memory cell may represent a logical low in response to the state of the first transistor being a logical high and the state of the second transistor being a logical low. In other embodiments, the particular complementary charge trap memory cell may include more than two transistors, and the logical value of the particular complementary charge trap memory cell may correspond to the respective states of each of the transistors.

The system may further include a first bitline and a second bitline. The first bitline may be coupled to the first transistor, and the second bitline may be coupled to the second transistor. A first power supply node may be configured to provide a first voltage to the first transistor, which may be configured to apply the first voltage to the first bitline. A second power supply node maybe configured to provide a second voltage to the second transistor, and the second transistor may be configured to apply the second voltage to the second bitline. The first voltage may be different than the second voltage.

Providing different voltages to the first transistor and the second transistor (e.g., applying the first voltage and the second voltage, respectively) may cause the particular complementary charge trap memory cell to evaluate to a known state (e.g., a logical high or a logical low). For example, by applying the first voltage and the second voltage, the first bitline may be pulled to a logical high while the second bitline may be pulled to a logical low. The corresponding logical state of the particular complementary charge trap memory cell may be a logical low. Since the logical state of the particular complementary charge trap memory cell is known to be a logical low, the output of the sense circuit may be tested to ensure that the output corresponds to the logical low.

For instance, the sense circuit may include a third transistor and a fourth transistor. The third transistor and the fourth transistor may both be larger (e.g., physically larger) than both the first transistor and the second transistor of the particular charge trap memory cell. The third transistor may be configured to pull the first bitline to a ground voltage in response to a voltage of the second bitline satisfying a voltage threshold associated with the third transistor. Conversely, the fourth transistor may be configured to pull the second bitline to a ground voltage in response to a voltage of the first bitline satisfying a voltage threshold associated with the fourth transistor.

According to a particular embodiment, the first voltage applied to the first transistor may be greater than or equal to the voltage threshold associated with the fourth transistor, and the second voltage that is applied to the second transistor may be less than the voltage threshold associated with the third transistor. As a result, the first transistor may apply the first voltage to the first bitline, which may activate the fourth transistor, and the fourth transistor may pull the second bitline to ground.

An output of the sense circuit may be compared with the known state of the complementary charge trap memory cell to test operation of the sense circuit. For instance, if the known state of the complementary charge trap memory cell corresponds to a logical high, the output of the complementary charge trap memory cell may be evaluated to ensure that an output voltage of the output also corresponds to a logical high.

FIG. 1 illustrates a particular embodiment of a system 100 for testing a charge trap memory. The system 100 may include one or more complementary charge trap memory cells 160, 162, and 164. It will be appreciated that while three complementary charge trap memory cells 160, 162, and 164 are illustrated, the system may include fewer or more complementary charge trap memory cells in other embodiments. Each of the complementary charge trap memory cells 160, 162, and 164 may include a pair of transistors. For instance, charge trap memory cell 160 may include transistor 108 a and transistor 108 b, charge trap memory cell 162 may include transistor 110 a and transistor 110 b, and charge trap memory cell 164 may include transistor 112 a and transistor 112 b. It will be appreciated that in other embodiments, each of the complementary charge trap memory cells 160, 162, and 164 may include more than two transistors.

Further, each of the complementary charge trap memory cells 160, 162, and 164 may be coupled to a corresponding wordline. For instance, wordline 102 may be coupled to transistor 108 a and transistor 108 b of complementary charge trap memory cell 160. Similarly, wordline 104 may be coupled to transistor 110 a and transistor 110 b of complementary charge trap memory cell 162, and wordline 106 may be coupled to transistor 112 a and transistor 112 b of complementary charge trap memory cell 164. Additionally, a first power supply node 114 may be coupled to transistors 108 a, 110 a, and 112 a, and a second power supply node 116 may be coupled to transistors 108 b, 110 b, and 112 b. Further, a first bitline 120 a may be coupled to transistors 108 a, 110 a, and 112 a, and a second bitline 120 b may be coupled to transistors 108 b, 110 b, and 112 b.

The complementary charge trap memory cells 160, 162, and 164 may be programmed in response to a programming indication received by the system 100. For example, in order to select a transistor for programming from transistors 108 a, 110 a, 112 a, 108 b, 110 b, and/or 112 b, the program driver 124 may activate transistors 122 a and 122 b, which may pull the first bitline 120 a and the second bitline 120 b down to a ground voltage. Further, in order to program the selected transistor, a voltage may be applied to a corresponding power supply node (e.g., the first power supply node 114 or the second power supply node 116). Additionally, a corresponding wordline (e.g., WL2 102, WL1 104, or WL0 106) may be activated to program the selected transistor. For example, in order to program transistor 110 a, the program driver 124 may cause the first bitline 120 a and the second bitline 120 b to be pulled to the ground voltage. A voltage (e.g., a programming voltage) may be applied to the first power supply node 114, and WL1 104 may be activated, which may cause current to flow through transistor 110 a. The current through transistor 110 a may cause the transistor 110 a to be programmed (e.g., a charge may be stored by transistor 110 a). In certain embodiments, the programming of transistor 110 a may cause a reading of the complementary charge trap memory cell 162 to correspond to a logical bit value of 1 or a logical high.

Additionally, transistors 126 a and 126 b may be configured to protect the sense circuit 170 from relatively high voltage during programming of the complementary charge trap memory cells 160, 162, and 164. Further, it will be appreciated that particular voltage and/or the second particular voltage may be the same or different than voltages that may be applied by the first power supply node 114 or the second power supply node 116 during read operations and/or test configuration operations, as described below. Moreover, in certain implementations, the particular voltage may be the same as the second particular voltage.

According to a particular embodiment, a sense circuit 170 may be coupled to the complementary charge trap memory cells 160, 162, and 164, such as via the first bitline 120 a and the second bitline 120 b. The sense circuit 170 may also include a pair of cross-coupled transistors, such as transistor 150 a and transistor 150 b. In certain implementations, transistor 150 a and transistor 150 b may be field-effect transistors (FETs). Further, the source/drain of transistor 150 a may be coupled to the first bitline 120 a while the gate of transistor 150 a may be coupled to the second bitline 120 b. Conversely, the source/drain of transistor 150 b may be coupled to the second bitline 120 b while the gate of transistor 150 b may be coupled to the first bitline 120 a. As such, transistor 150 a may be configured to pull the first bitline 120 a to a ground voltage in response to a second bitline voltage corresponding to the second bitline 120 b satisfying a voltage threshold associated with transistor 150 a. Similarly, transistor 150 b may be configured to pull the second bitline 120 b to a ground voltage in response to a first bitline voltage corresponding to the first bitline 120 a satisfying a voltage threshold associated with transistor 150 b. Further, the voltage threshold associated with transistor 150 a may be the same or approximately the same as the voltage threshold associated with transistor 150 b. In addition, both transistor 150 a and transistor 150 b may be larger than each of the transistors included in the complementary charge trap memory cells 160, 162, and 164 (e.g., transistors 108 a, 108 b, 110 a, 110 b, 112 a, and 112 b).

During a normal read operation (e.g., a read operation that is performed while the system 100 is not in a test configuration state), a memory cell (e.g., memory cells 160, 162, or 164) may be selected for reading. A wordline (e.g., wordlines 102, 104, or 106) corresponding to the memory cell may be activated and a voltage may be applied to the transistors included in the memory cell. Applying the voltage may cause the transistors to be activated, thereby causing the voltage corresponding to the first bitline 120 a and the voltage corresponding to the second bitline 120 b to begin increasing. In response to the increases of the voltages corresponding to the first bitline 120 a and the second bitline 120 b, the sense circuit 170 may cause one of the first bitline 120 a or the second bitline 120 b to be pulled to a logical low and may cause the other bitline to be pulled to a logical high.

For instance, complementary charge trap memory cell 162 (hereinafter “memory cell” 162) may be selected for reading. Depending on the logical state of the memory cell 162, either transistor 110 a or transistor 110 b may store a charge. According to a particular embodiment, if transistor 110 a stores a charge and transistor 110 b does not store a charge, the logical state of the memory cell 162 is a logical high. Conversely, if transistor 110 a does not store a charge and transistor 110 b stores a charge, the logical state of the memory cell 162 is a logical low.

In order to select memory cell 162 for the normal read operation, a voltage (e.g., Vdd) may be applied to both transistors 110 a and 110 b. The voltage applied to wordline 104 may be associated with a wordline slew corresponding to a rate of voltage change over time. For example, the wordline slew may cause the voltage applied to the wordline 104 to increase from 10% Vdd to 90% Vdd in about 200-800 picoseconds. According to a particular embodiment, during a normal read operation, Vdd may be supplied by the first power supply node 114. As such, during the normal read operation, the first power supply node 114 may be coupled to both transistors 110 a and 110 b, such as via a switch (not pictured). For instance, FIG. 2 depicts a circuit diagram representation of the system 100 during the normal read operation where the first power supply node is coupled to both transistors 110 a and 110 b. According to another particular embodiment, during the normal read operation, Vdd may be independently supplied by the first power supply node 114 and the second power supply node 116.

Applying the voltage to transistors 110 a and 110 b may activate transistors 110 a and 110 b. Activation of transistor 110 a may cause a voltage corresponding to the first bitline 120 a to increase toward Vdd. Similarly, activation of transistor 110 b may cause a voltage corresponding to the second bitline 120 b to increase toward Vdd. Further, since transistor 110 a is storing charge and transistor 110 b is not storing charge, the voltage threshold corresponding to transistor 110 a may be larger than the voltage threshold corresponding to transistor 110 b. Therefore the voltage, changing at a rate based on the wordline slew, reaches the threshold voltage of transistor 110 b before reaching the threshold voltage of transistor 110 a, which causes the voltage corresponding to the second bitline 120 b to begin increasing toward Vdd before the voltage corresponding to the first bitline 120 a begins increasing.

Since the voltage corresponding to the second bitline 120 b begins increasing before the voltage corresponding to the first bitline 120 a begins increasing, and the respective voltage thresholds of transistors 150 a and 150 b are equal or approximately equal, transistor 150 a is activated before transistor 150 b can be activated. Activation of transistor 150 a may cause the first bitline 120 a to be pulled to a ground voltage (e.g., due to transistor 150 a being larger than transistor 110 a). Because the first bitline 120 a is pulled to ground, the first bitline 120 a is unable to activate transistor 150 b, and transistor 150 b remains inactivated. As a result, the first bitline 120 a is pulled to a logical low (e.g., the ground voltage), and the second bitline 120 b is allowed to eventually be pulled to a logical high (e.g., Vdd). Furthermore, inverter 144 a may reverse the logical low of the first bitline 120 a and cause the output node 146 of the sense circuit 170 to evaluate to a logical high, and inverter 144 b may reverse the logical low of the second bitline 120 b and cause the complementary output node 148 of the sense circuit 170 to evaluate to a logical low. The logical state of the output node 146 may correspond to the logical state of the memory cell 162.

Additionally, inverters 140 a and 140 b may be configured to pull the faster rising bitline to a voltage of the Vdd rail. Using the example above, since the voltage corresponding to the second bitline 120 b increases faster than the voltage corresponding to the first bitline 120 a, inverter 140 b pulls the second bitline 120 b to the voltage of the Vdd rail by reversing the logical high of the second bitline 120 b to a logical low. The logic low output of the inverter 140 b may activate transistor 142 b, which may cause the voltage corresponding to the second bitline 120 b to be pulled to the voltage of the Vdd rail. Conversely, in situations where the voltage corresponding to the first bitline 120 a increase faster than the voltage corresponding to the second bitline 120 b, inverter 140 a pulls the first bitline 120 a to the voltage of the Vdd rail by reversing a logical high of the first bitline 120 a to a logical low. The logic low output of the inverter 140 a may activate transistor 142 a, which may cause the voltage corresponding to the first bitline 120 a to be pulled to the voltage of the Vdd rail.

According to a particular embodiment, the sense circuit 170 may be tested prior to programming of the complementary charge trap memory cells 160, 162, and 164. As such, before programming, the logical state of the complementary charge trap memory cells 160, 162, and 164 may be unknown. For instance, due to certain imperfections in fabrication and/or manufacturing, there may be variations in the respective voltage thresholds of the transistors in the complementary charge trap memory cells 160, 162, and 164 (e.g., transistors 108 a, 108 b, 110 a, 110 b, 112 a, and 112 b). Such variations may also be unknown or difficult to determine prior to programming of the complementary charge trap memory cells 160, 162, and 164. Thus, since the respective voltage thresholds are used to determine the logical states of the complementary charge trap memory cells 160, 162, and 164, the logical states of the complementary charge trap memory cells 160, 162, and 164 are also unknown prior to being programmed.

Thus, the system 100 of FIG. 1 may be configured to cause one or more of the complementary charge trap memory cells 160, 162, and 164 to evaluate to a known logical state prior to being programmed. The known logical state may then be compared against an output of the sense circuit 170. According to a particular embodiment, in order to initiate a testing operation of the sense circuit 170, the system 100 may receive a test configuration indication indicating that the system 100 is in a testing operation mode. For example, the signal may be received from a memory controller or any other device. In response to the testing operation mode, the first bitline 120 a and the second bitline 120 b may be precharged to a ground voltage, such as via a precharge signal node 132. Further, the first power supply node 114 may be configured to provide a first voltage to the first bitline 120 a and the second power supply node 116 may be configured to provide a second voltage to the second bitline 120 b. A third voltage may be applied to a wordline corresponding to a particular complementary charge trap memory cell that is to be read during testing. The third voltage may activate a first transistor and a second transistor in the particular complementary charge trap memory cell.

As a result, upon activation, the first transistor may be configured to pull the voltage corresponding to the first bitline 120 a toward the first voltage. Similarly, the second transistor may be configured to pull the voltage corresponding to the second bitline 120 b toward the second voltage. Further, the first voltage may be different from the second voltage, and the voltage difference may cause one of the first bitline 120 a or the second bitline 120 b to be pulled to a logical low while the other bitline is pulled to a logical high. Thus, by applying different voltages to the first bitline 120 a and the second bitline 120 b, a known logical state of the particular complementary charge trap memory cell can be simulated. For instance, consider a test operation in which due to the first voltage and the second voltage applied to the first bitline 120 a and the second bitline 120 b, respectively, the first bitline 120 a is pulled to a logical low and the second bitline 120 b is pulled to a logical high. Such a test operation may simulate a situation where the first transistor is storing charge and the second transistor is not storing charge (e.g., the first transistor is simulated to have a greater voltage threshold than the second transistor). The first transistor storing charge and the second transistor not storing charge may correspond to a known logical state of the particular complementary charge trap memory cell. As such, the output node 146 of the sense circuit 170 may then be tested against the known logical state of the particular complementary charge trap memory cell.

More specifically with respect to FIG. 1, according to a particular embodiment, the first bitline 120 a and the second bitline 120 b may be precharged to a ground voltage during testing operation of the sense circuit. For instance, precharge signal node 132 may activate transistor 128, which may be configured to balance the first bitline 120 a and the second bitline 120 b. The precharge signal node 132 may also activate transistor 130 a and transistor 130 b. Transistor 130 a may be configured to pull the first bitline 120 a to the ground voltage, and transistor 130 b may be configured to pull the second bitline 120 b to the ground voltage. Thus, the precharge signal node 132 may be configured to precharge the first bitline 120 a and the second bitline 120 b to the ground voltage (e.g., via transistors 130 a and 130 b) prior to the first power supply node 114 applying voltage to the first bitline 120 a and prior to the second power supply node 116 applying voltage to the second bitline 120 b.

After precharging the first bitline 120 a and the second bitline 120 b, the first power supply node 114 may apply a first voltage to the first bitline 120 a (e.g., via at least one of transistors 108 a, 110 a, and 112 a), and the second power supply node 116 may apply a second voltage to the second bitline 120 b (e.g., via at least one of transistors 108 b, 110 b, and 112 b). For example, the first power supply node 114 may provide the first voltage to at least one of transistors 108 a, 110 a, and 112 a, and at least one of transistors 108 a, 110 a, and 112 a may apply the first voltage to the first bitline 120 a. Similarly, the second power supply node 116 may provide the second voltage to at least one of transistors 108 b, 110 b, and 112 b, and at least one of transistors 108 b, 110 b, and 112 b may apply second first voltage to the second bitline 120 b To illustrate, the first voltage may be 1 Volt (V), and the second voltage may be 0V. Memory cell 160 may be selected for testing by applying a third voltage to wordline 102. Further, applying the first voltage (e.g., 1V) to the first bitline 120 a and applying the second voltage (e.g., 0V) to the second bitline 120 b may ensure that the second bitline 120 b remains low while the first bitline 120 a is eventually pulled high. For instance, transistor 108 a may be activated due to the first voltage while the second voltage may be insufficient to activate transistor 108 b. In other words, transistor 108 a may be activated before transistor 108 b is activated (e.g., since the second voltage is too low to activate transistor 108 b), which may simulate a state in which transistor 108 a is not storing charge and transistor 108 b is storing charge, thereby corresponding to a known logical state of memory cell 160.

Further, while the second bitline 120 b remains low, the first bitline 120 a may be pulled high via activation of transistor 108 b in memory cell 160. Due to the first bitline 120 a being pulled high and the second bitline 120 b remaining low, transistor 150 b may be activated, and transistor 150 a may remain inactivated. Activation of transistor 150 b may cause the second bitline 120 b to be grounded (e.g., to remain low via the ground). The grounded state (e.g., low state) of the second bitline 120 b is insufficient to activate transistor 150 a, which may enable the first bitline 120 a to remain high. The signal of the first bitline 120 a may be inverted at inverter 144 a and provided to the output node 146. The output node of 146 may then be compared to the known simulated logical state of the memory cell 160 to test whether the sense circuit 170 is operating correctly.

FIG. 3 illustrates a method 300 for testing charge trap memory cells according to a particular embodiment. The method 300 may include applying a first voltage to a first bitline via a first transistor of a charge trap memory cell, at 302. For example, the first power supply node 114 may be configured to provide the first voltage to transistor 108 a, 110 a, or 112 a. Transistor 108 a, 110 a, or 112 a may be configured to apply the first voltage to the first bitline 120 a.

At 304, the method 300 may include applying a second voltage to a second bitline via a second transistor of the charge trap memory cell. For example, the second power supply node 116 may be configured to provide the second voltage to transistor 108 b, 110 b, or 112 b. Transistor 108 b, 110 b, or 112 b may be configured to apply the second voltage to the second bitline 120 b.

At 306, the method may include outputting, prior to programming of the charge trap memory cell, a logical high signal or a logical low signal in response to applying the first voltage to the first bitline and the second voltage to the second bitline. For example, applying a first voltage to the first bitline 120 a and a second voltage to the second bitline 120 b may cause the first bitline 120 a to evaluate to a logical high or a logical low and the second bitline 120 b to evaluate to the logical state opposite of the first bitline 120 a. The logical state of the first bitline 120 a may be output at the output node 146, which may correspond to a logical state of at least one of the charge trap memory cells 160, 162 and 164.

The system and method described by FIG. 1 and FIG. 3 may enable one or more of the charge trap memory cells 160, 162, and 164 to evaluate to a known state. As described above, by applying different voltages to the first bitline 120 a and the second bitline 120 b, a known logical state of a particular complementary charge trap memory cell can be simulated. If the logical state of the particular complementary charge trap memory cell is known, the output node 146 of the sense circuit 170 may be tested against the known logical state in order to reliably test the operations of the sense circuit 170, the charge trap memory cells 160, 162, and 164, and/or other components of the system 100.

Referring to FIG. 4, an illustrative system 400 including a computer 410 is shown. The computer 410 may be an implementation of a computing system that includes the complementary charge trap memory system 100 of FIG. 1. The computer 410 includes at least one computer processor (CPU) 414 as well as main memory 402, a memory controller 401, and a non-volatile memory 460. At least one of the main memory 402 or the non-volatile memory 460 may include the complementary charge trap memory system 100 of FIG. 1. In some implementations, the memory controller 401 may include one or more components of the sense circuit 170 of FIG. 1. The main memory 402 is connected through a memory bus 408 to the memory controller 401. The memory controller 401 and the non-volatile memory 460 are connected through a second memory bus 416 and a bus adapter 418 to the processor 414 through a processor bus 434.

Stored at the memory 402 is an application 420 that may be a module of user-level computer program instructions for carrying out particular tasks (e.g., testing of the memory system 100). Also stored at the main memory 402 is an operating system 422. Operating systems include, but are not limited to, UNIX® (a registered trademark of The Open Group), Linux® (a registered trademark of Linus Torvalds), Windows® (a registered trademark of Microsoft Corporation, Redmond, Wash., United States), AIX® (a registered trademark of International Business Machines (IBM) Corp., Armonk, N.Y., United States) i5/OS® (a registered trademark of IBM Corp.), and others as will occur to those of skill in the art. The operating system 422 and the application 420 in the example of FIG. 4 are shown in the main memory 402, but components of the aforementioned software may also, or in addition, be stored at non-volatile memory (e.g., on data storage, such as data storage 424 and/or the non-volatile memory 460).

The computer 410 includes a disk drive adapter 438 coupled through an expansion bus 440 and the bus adapter 418 to the processor 414 and other components of the computer 410. The disk drive adapter 438 connects non-volatile data storage to the computer 410 in the form of the data storage 424 and may be implemented, for example, using Integrated Drive Electronics (“IDE”) adapters, Small Computer System Interface (“SCSI”) adapters, Serial Attached SCSI (“SAS”) adapters, and others as will occur to those of skill in the art. Non-volatile computer memory also may be implemented as an optical disk drive, electrically erasable programmable read-only memory (so-called “EEPROM” or “Flash” memory), RAM drives, and other devices, as will occur to those of skill in the art. In a particular embodiment, the data storage 424 may store the data and information described herein.

The computer 410 also includes one or more input/output (“I/O”) adapters 442 that implement user-oriented input/output through, for example, software drivers and computer hardware for controlling input and output to and from user input devices 444, such as keyboards and mice. In addition, the computer 410 includes a communications adapter 446 for data communications with a data communications network 450. The data communications may be carried out serially through Recommended Standard 232 (RS-232) connections (sometimes referred to as “serial” connections), through external buses such as a Universal Serial Bus (“USB”), through data communications networks such as internet protocol (IP) data communications networks, and in other ways as will occur to those of skill in the art. The communications adapter 446 implements the hardware level of data communications through which one computer sends data communications to another computer, directly or through a data communications network. Examples of the communications adapter 446 suitable to use in the computer 410 include, but are not limited to, modems for wired dial-up communications, Ethernet (Institute of Electrical and Electronics Engineers (IEEE) 802.3) adapters for wired network communications, and IEEE 802.11 adapters for wireless network communications. The computer 410 also includes a display adapter 432 that facilitates data communication between the bus adapter 418 and a display device 430, enabling the application 420 to visually present output on the display device 430.

Particular embodiments described herein may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment containing both hardware and software elements. In a particular embodiment, the disclosed methods are implemented in software that is embedded in processor readable storage medium or storage device and executed by a processor that includes but is not limited to firmware, resident software, microcode, etc.

Further, embodiments of the present disclosure, may take the form of a computer program product accessible from a computer-usable or computer-readable storage device providing program code (e.g., computer-executable instructions) for use by or in connection with a computer, processor, or any instruction execution system. For the purposes of this description, a computer-usable or computer-readable storage device can be any apparatus that can tangibly embody a computer program and that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, processor, apparatus, or device.

In various embodiments, the medium can include an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. Examples of a computer-readable storage device include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) and digital versatile disk (DVD).

A data processing system suitable for storing and/or executing program code may include at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements can include local memory employed during actual execution of the program code, bulk storage, and cache memories that may provide temporary or more permanent storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution.

Input/output or I/O devices (including but not limited to keyboards, displays, pointing devices, etc.) can be coupled to the data processing system either directly or through intervening I/O controllers. Network adapters may also be coupled to the data processing system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modems, and Ethernet cards are just a few of the currently available types of network adapters.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the disclosed embodiments. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope possible consistent with the principles and features as defined by the following claims. 

The invention claimed is:
 1. A circuit for testing a memory, the circuit comprising: a complementary charge trap memory cell including a first transistor and a second transistor, a logical value of the complementary charge trap memory cell corresponding to respective states of the first transistor and the second transistor; a first bitline coupled to the first transistor, the first transistor configured to apply a first voltage to the first bitline; a second bitline coupled to the second transistor, the second transistor configured to apply a second voltage to the second bitline; and a sense circuit configured to output, prior to programming of the complementary charge trap memory cell, a logical high signal or a logical low signal in response to the first transistor applying the first voltage to the first bitline and the second transistor applying the second voltage to the second bitline.
 2. The circuit of claim 1, further comprising: a power supply configured to, in response to a programming indication, apply a third voltage to the first bitline and to the second bitline to program the complementary charge trap memory cell.
 3. The circuit of claim 1, wherein the first transistor applies the first voltage to the first bitline and the second transistor applies the second voltage to the second bitline in response to a test configuration indication.
 4. The circuit of claim 1, wherein the sense circuit further comprises: a third transistor configured to pull the second bitline toward a ground voltage in response to a first bitline voltage corresponding to the first bitline satisfying a first voltage threshold; and a fourth transistor configured to pull the first bitline toward the ground voltage in response to a second bitline voltage corresponding to the second bitline satisfying a second voltage threshold.
 5. The circuit of claim 1, wherein the first transistor and the second transistor are field effect transistors.
 6. The circuit of claim 1, wherein the first bitline is coupled to a first power supply and the second bitline is coupled to a second power supply.
 7. The circuit of claim 1, wherein the sense circuit further comprises: a third transistor configured to pull the first bitline toward a ground voltage prior to the first transistor applying the first voltage to the first bitline; and a fourth transistor configured to pull the second bitline toward the ground voltage prior to the second transistor applying the second voltage to the second bitline.
 8. The circuit of claim 1, further comprising: a first inverter coupled to the first bitline; and a third transistor coupled to an output of the first inverter, the third transistor configured to pull the first bitline up to a supply voltage in response to the output of the first inverter satisfying a first voltage threshold associated with the third transistor.
 9. The circuit of claim 8, further comprising: a second inverter coupled to the second bitline; and a fourth transistor coupled to an output of the second inverter, the fourth transistor configured to pull the second bitline up to the supply voltage in response to the output of the second inverter satisfying a second voltage threshold associated with the fourth transistor.
 10. A method for testing a memory cell, the method comprising: applying a first voltage to a first bitline via a first transistor of a charge trap memory cell; applying a second voltage to a second bitline via a second transistor of the charge trap memory cell; and outputting, prior to programming of the charge trap memory cell, a logical high signal or a logical low signal in response to applying the first voltage to the first bitline and the second voltage to the second bitline.
 11. The method of claim 10, further comprising applying, in response to a programming indication, a third voltage to the first bitline and to the second bitline to program one or more cells of the charge trap memory cell.
 12. The method of claim 10, further comprising receiving a test configuration indication, wherein the first voltage is applied to the first bitline and the second voltage is applied to the second bitline in response to receiving the test configuration indication.
 13. The method of claim 10, further comprising: pulling the second bitline toward a ground voltage in response to a first bitline voltage corresponding to the first bitline satisfying a first voltage threshold; and pulling the first bitline toward the ground voltage in response to a second bitline voltage corresponding to the second bitline satisfying a second voltage threshold.
 14. The method of claim 10, further comprising: providing the first voltage to the first bitline via a first power supply; and providing the second voltage to the second bitline via a second power supply.
 15. The method of claim 10, further comprising: pulling the first bitline toward a ground voltage prior to the first transistor applying the first voltage to the first bitline; and pulling the second bitline toward the ground voltage prior to the second transistor applying the second voltage to the second bitline. 